Bistable storage tube having photosensitive phosphor storage dielectric,apparatus and method of storing light image by such tube



Feb. 4, 1969 I-I. J. MEPHAM 3,426,236

B ISTABLE STORAGE TUBE HAVING PHOTOSENSITIVE PHOSPHOR STORAGE DIELECTRIC, APPARATUS AND METHOD OF STORING LIGHT IMAGE BY SUCH TUBE Filed March 26, 1965 VERT. 68 C HORIZONTAL TRIGGVER 82 73 I r 98 GEN HOR f 92 RASTER SWEEI Z-AXIS GEN. I INPUT V'ERTICAL INPUT 3025 V. 305OV.

I +500 v. WRITE R EAD WRITE READ WRITE READ 94 74 w F 3 SOURCE +50Ovv I T 1 62 -3ooo 34 L 36 v 90 +50v 96 t STORE BINTEGRATE 66 25v v F- ouT 68 m6 STORAGE Z 50 ,2 was we CQ'EII IAQ ED LIGHT l X'RAY SOURCE SOURCE A /0 0 Fig.2 (@QQ) 70 p laaf/ STORAGE 20 24 TUBE //2 /638 42 40 FF 4 k g f 1 /22 -I \JQAAILAAAAHA BUCKHOR/V, BLORE, KLAROU/ST 8 SPAR/(MAN ATTORNEYS United States Patent BISTABLE STORAGE TUBE HAVING PHOTOSEN- SITIVE PHOSPHOR STORAGE DIELECTRIC, AP- PARATUS AND METHOD OF STORING LIGHT IMAGE BY SUCH TUBE Herbert J. Mepham, Portland, Oreg., assignor to Tektronix, Inc., Beaverton, Oreg., a corporation of Oregon Filed Mar. 26, 1965, Ser. No. 443,150 US. Cl. 315-12 12 Claims Int. Cl. H01j 29/41 ABSTRACT OF THE DISCLOSURE A charge image storage apparatus is described which employs a direct viewing bistable storage tube having a photosensitive storage dielectric of phosphor material. The storage apparatus includes means for directing a light image and an electron image onto the storage dielectric to produce corresponding charge images thereon which may be stored bistably. The storage tube may be provided with electrical readout to a remote television monitor in addition to the optical readout provided by the light images emitted by the phosphor storage dielectric.

The subject matter of the present invention relates generally to electrical charge image storage apparatus and methods of operating such apparatus, and in particular to storage apparatus including a bistable storage tube having a storage target with a photosensitive storage dielectric of phosphor material as well as means for directing a light image and an electron image onto the storage dielectric in order to produce corresponding charge images on such dielectric which are stored bistably and methods of operating such apparatus. In addition, the present storage apparatus may also have a means for transmitting an electrical readout signal corresponding to the charge image from the storage tube to a remote display device in order to reproduce the original light image on such display device.

Briefly, the storage target in the apparatus of the present invention may be a direct viewing bistable storage target having a photosensitive storage dielectric which is in the form of an integral, porous layer of phosphor material supported over a light transparent electrically conductive coating on one side of a light transparent electrically insulative support plate. This phosphor layer has a sufficiently porous structure to enable secondary electrons emitted from one side of the layer to be transmitted through the layer and collected by the conductive coating on the other side of such layer, and is of the proper thickness to enable bistable storage of the charge image on the phosphor layer for a controllable time. The storage target may be similar to that described in copending US. patent application Ser. No. 180,457, filed Mar. 19, 1962, now US. patent 3,293,472, and US. patent application Ser. No. 214,877, filed Aug. 6, 1962, now US. patent 3,214,631, both by Robert H. Anderson.

The storage apparatus and method of the present invention are especially useful in connection with a storage type of cathode ray oscilloscope to store light images directed onto the photosensitive storage dielectric of the storage tube and superimposed on electron beam images of electrical signal waveforms also stored on such storage dielectric. These light images may be the image of a graticule scale for measuring the dimensions of the electrical signal waveform, the image of a Written document, the image of a map providing the geographical background of a radar display, or the image of a previously recorded electrocardiogram of a doctors patient, to illustrate but a few of the uses of such apparatus. In

3,426,236 Patented Feb. 4, 1969 ice addition, the present storage apparatus and method can also be employed ot convert an X-ray image into a visible light image while simultaneously producing a charge image on the storage dielectric which is stored and may also be converted into an electrical readout signal for transmission to a remote display device. Furthermore, a less intense light source may be employed to form a pointer spot" on the photosensitive storage dielectric, whose charge image does not have sufiicient potential to store but does produce an electrical readout signal to enable the pointer spot to be reproduced on a remote television monitor for identifying to monitor observers particular portions of an electrical signal waveform stored on the storage target.

The storage apparatus and method of the present invention have several advantages over conventional light image storage apparatus and methods including a simpler, more reliable and more versatile operation. Thus, by employing a photosensitive storage dielectric the present apparatus can store a light image for a long controllable time without requiring a photocathode to first convert the light image into an electron image, as in previous bistable storage tubes. In addition, the storage apparatus of the present invention may employ a phosphor storage dielectric to provide a direct viewing storage target of simple, rugged and inexpensive construction which is photosensitive and emits a light image corresponding to the charge image stored thereon. Also, by projecting a light image of a graticule scale onto the storage target and storing such graticule image, it is possible to focus the graticule image in the plane of the storage dielectric to eliminate the parallax distortion associated with graticules outside of the storage tube, and to reproduce the graticule scale on a remote display device by transmitting an electrical readout signal from the storage target to such display device. It is also possible to form light images of the positions of selector switches controlling the vertical sensitivity and the horizontal sweep speed of the oscilloscope to store the units of the graticule scale in terms of volts per centimeter and seconds per centimeter on the storage target for electrical readout to the monitor. This enables persons viewing the remote television monitor or other display device to determine the characteristics of an electrical signal waveform stored on the storage tube and reproduced on the display device in a position superimposed on the graticule image.

Another advantage of the present apparatus and method is that a low intensity light source may be employed as a means of forming the stored light images because light images of law intensity or short duration which would ordinarily not produce charge images of sufficient potential for storage, may be stored by preventing the low velocity fiood electrons in the storage tube from striking the storage dielectric during the time the light image is irradiating such storage dielectric. This enables a low intensity or short duration light image to increase the potential of its charge image above the minimum voltage necessary for bistable storage in a manner similar to the method of charge image integration discussed in copending United States patent application Ser. No. 302,880, filed Aug. 19, 1963, by Robert H. Anderson and entitled, Improved Storage Tube and Method of Operation. The method and apparatus of the present invention also enables storage of X-ray images and produces light images corresponding to the stored X-ray images, thereby reducing the X-ray dosage received by the irradiated object.

In addition, it has been found that the light image of an internal graticule scale provided on the inner surface of the face plate of the storage tube beneath the transparent conductive areas and photosensitive storage dielectric of the storage target can be stored. This is accomplished merely by transmitting a flash of light of high lntenslty through the outer edge of the face plate to illum nate the graticule and produce a charge image of such graticule on the storage dielectric of suflicient potential to store.

It should be noted that the photosensitive phosphor storage dielectric is sensitive to invisible as well as v1s1ble light and may be employed to store an ultraviolet or X-ray image. Therefore the term light is intended to refer to such invisible light as well as to visible light in the present application.

It is therefore one object of the present invention to provide an improved charge storage apparatus and method for storing light images of low intensity or short duration.

Another object of the invention is to provide charge storage apparatus and method of operation for storing a light image on a photosensitive storage dielectric as a charge image and reproducing such light image on a remotely positioned display device by transmitting an electrical readout signal corresponding to the charge image to such display device.

A further object of the present invention is to provide an improved storage apparatus and method in which both a light image and an electron beam image are stored simultaneously on a storage target.

An additional object of the invention is to provide an improved storage apparatus in which a photosensitive layer of phosphor material is employed as the storage dielectric in order to provide a direct viewing storage target of simple and inexpensive construction.

Still another object of the present invention is to provide an improved method of operation of a charge storage apparatus in which a pointer spot of low intensity light is directed onto a photosensitive storage dielectric in order to produce a charge image of insufficient potential to store but of suflicient potential to be reproduced on a remote display device by electrical readout in order to indicate different portions of another charge image stored on said storage dielectric and reproduced on such display device.

A still further object of the invention is to provide an improved charge storage apparatus and method for directing a light image of a graticule scale onto a photosensitive storage dielectric, for storing such graticule image, and for reproducing such graticule image on a remote display device by transmitting an electrical readout singal corresponding to such stored graticule image to such display device in order to measure the characteristics of an electrical signal waveform stored on such storage dielectric and reproduced on the display device by the electrical readout signal.

Other objects and advantages of the present invention will be apparent from the following detailed description of several preferred embodiments thereof and from the attached drawings, of which:

FIG. 1 is schematic diagram of a charge storage apparatus in accordance with one embodiment of the present invention;

FIG. 2 is a schematic diagram of a modification of the storage apparatus of FIG. 1 in accordance with another embodiment of the invention;

FIG. 3 is a schematic diagram of a further modification of the apparatus of FIG. 1 in accordance with still anther embodiment of the present invention; and

FIG. 4 is a partially schematic view showing an enlarged portion of the storage tube of FIG. 1 in cross section, along with apparatus for illuminating a graticule scale provided inside such tube to produce a graticule light image of suflicient intensity to be stored.

As shown in FIG. 1 the charge image storage apparatus of the present invention includes a storage tube 10, which may be of a direct viewing bistable type similar to that shown in copending US. patent application Ser. No. 214,877, filed by Robert H. Anderson on Aug. 6, 1962.

The storage tube has a storage target 12 mounted inside an evacuated envelope 14 on the inner surface of the transparent glass face plate portion 16 of such envelope at one end of the tube. A main electron gun, including a cathode 18, a control grid 20 and a focusing and accelerating structure 22, is also mounted inside the envelope of the storage tube at the opposite end of the tube from the storage target. The electron beam produced by the electron gun including cathode 18 is deflected by a pair of horizontal deflection plates 24 and a pair of vertical deflection plates 26 positioned between such electron gun and the storage target 12 in a conventional manner.

In addition, the storage tube is provided with one or more flood type electron guns, each having a cathode 28, a control grid 30 and an anode 32, which are supported inside the envelope 14 adjacent the output end of the vertical deflection plates 26, so that the electrons emitted from such flood guns are focused into a Wide beam and substantially uniformly distributed over the storage target 12. A plurality of focusing and collimating electrodes may also be provided in the form of longitudinally spaced wall bands coated on the inner surface of the envelope 10 between the flood guns and the storage target, which are represented in FIG. 1 for the sake of simplicity by a single wall band electrode 34. The wall band electrodes focus the flood electrons onto the surface of the storage target 12 and collimate such electrons so that they strike such target at approximately right angles thereto to prevent spreading of the charge image stored on such target.

The storage target 12 includes a photosensitive storage dielectric 36, which may be an integral layer of P-1 type phosphor material supported over a light transparent electrically conductive coating of tin oxide or other suitable material on the inner surface of the face plate 16. This conductive coating is divided into two conductive areas 38 and 40 of substantially the same size, which are insulatingly spaced from each other by a gap 42 extending horizontally completely across the face plate 16. The face plate 16 is sealed to a ceramic funnel portion 44 of the envelope by a fused glass frit seal 46 and the conductive areas 38 and 40 extend through such seal to the exterior of the envelope, as shown in FIG. 4. This construction enables different potentials to be applied to the conductive areas 38 and 40 in order to provide a split screen storage tube in which the portion of the phosphor storage dielectric 36 above one conductive area can be operated in a storage mode, while the other portion of the phosphor layer is operated in a nonstorage mode. The phosphor storage dielectric emits a light image corresponding to the charge image stored on such dielectric.

The phosphor storage dielectric 36 has a sufficiently porous structure to enable secondary electrons emitted from the bombarded surface of such phosphor layer to be transmitted through the phosphor layer and collected by the conductive areas 38 and 40 on the opposite slde thereof and a thickness within a critical range of thicknesses over which the phosphor material is capable of bistable storage. Since the phosphor storage dielectric is photosensitive, a light image directed onto the storage dielectric produces a charge image on such storage dielectric corresponding to such light image, Thus, if a light image of suflicient intensity is directed onto the phosphor storage dielectric 36, the charge image produced by such light image is of a high enough potential to enable bistable storage of such charge image for a controllable time. In order to enhance the photosensitive characteristics of the phosphor storage dielectric, photoemissive material such as magnesium oxide or a photoconductive material such as cadmium sulphide may be uniformly mixed throughout the phosphor layer which enables storage of light images of lower intensity.

In one embodiment of the invention a light image is projected onto the photosensitive storage dielectric 36 by means of an external light source 48 of high intensity such as an arc lamp, film slide projector, or a photographic flash unit, a light mask 50 such as a photographic film negative, and a focusing lens 52 positioned in the order named in front of the face plate of the storage tube. Thus the light image of the film negative 50 is focused onto the storage dielectric and the resulting charge image stored. The film negative can contain the image of a graticule scale, a map of a geographical area, the page of a book or other document, an electrocardiogram or other medical diagram.

In addition, a pointer light source 54, producing a narrow light beam of low intensity, may be provided to direct a small spot of light onto the photosensitive storage dielectric 36 and produce a charge image of such spot, having insufficient potential to be stored but sufficient potential to produce an electrical readout signal during the reading operation of the storage tube hereafter described. Thus, the pointer light spot may be used to indicate different portions of an electrical signal waveform, or other image stored on the storage dielectric 36, to a person observing a reproduction of such stored charge image on a remotely positioned monitor device 56 such as a television receiver tube or a storage tube similar to tube 10.

The control grid or other Z-axis input of the monitor tube 56 is connected through an amplifier 58 to both of the conductive areas 38 and 40 of the storage target 12 in the storage tube 10. The conductive areas 38 and 40 are also connected to sources of positive D.C. supply voltage of about +500 volts through variable resistances 60 and 62 respectively, which are connected to ground through fixed resistances 64 and 66 respectively. Thus, the settings of the variable resistors 60 and 62 control the DC. currents flowing through resistors 64 and 66 and the voltages produced at output terminals 68 and 70 which are connected to the conductive areas 36 and 40 of the storage target. The cathodes 28 of the flood guns are normally connected to 0 volts or ground potential, so that a voltage of about +200 volts applied to the conductive areas 38 and 40 is sufficient to cause the phosphor storage dielectric above such areas to store a bistable charge image. This voltage is between the fade positive voltage above which storage is not possible and the retention threshold voltage corresponding to the first cross-over voltage of the secondary emission characteristic of the storage dielectric, below which storage is not possible.

During the writing operation of the storage tube an electron beam image is directed onto the storage target by connecting the vertical deflection plates 26 to a vertical amplifier 72 by means of a selector switch 74 in the write position of such switch. This enables vertical input signals applied to an input terminal 76 of such vertical amplifier to be applied to the vertical deflection plates. In addition, the horizontal deflection plates 24 of the storage tube are connected to a horizontal sweep generator 78 by means of a selector switch 80 in the write position of such switch. The horizontal sweep generator may be triggered by the vertical input signal and is connected through a trigger generator 82 to the input terminal 76. If such a triggered sweep generator is employed, the vertical amplifier 72 may be provided with a delay line to prevent the vertical input signal from reaching the vertical deflection plates before the sweep signal is applied to the horizontal deflection plates. In addition, if the same electron gun is employed for both the reading and writing operations, it is necessary to either increase the velocity or the current density of the electron beam during writing. An increase in current density is preferred in order to enable the cathode 18 to remain at a constant negative DC. potential of about 3000 volts. The increase in current density of the writing electron beam is accomplished by connecting the control grid to a source of negative D.C. supply voltage of about 3025 volts by a selector switch 84 in the write position of such selector switch, which voltage is less negative that the 30S0 volts of the control grid in the read position of switch 84.

When employing a split screen type storage tube, a reference signal waveform may be first written on the lower half of the storage target 36 and stored so that such reference signal waveform is later reproduced as a light image 86 in a similar location on the viewing screen of the monitor sube 56 during the reading operation hereafter described. The charge image of the reference signal is stored on the storage dielectric 36 if the voltage of the conductive area 40 is between the retention threshold voltage and the fade positive voltage. After the reference signal is stored on the storage target 12, a comparison signal waveform may be written on the upper portion of the storage dielectric 36 over conductive area 38, whose voltage may be adjusted below the retention threshold level so that the comparison signal waveform is not stored but is merely compared with the reference signal waveform. If desired, the charge image of the waveform of the comparison signal may be stored merely by raising the voltage of the conductive area 38 above the retention threshold, and may then be reproduced as comparison signal image 88 on the viewing screen of the monitor tube 56 during electrical readout.

In order to indicate the characteristics of the waveforms 88 and 86 reproduced on the monitor tube 56, a light image of a graticule scale on the film negative 50 is projected onto the photosensitive storage dielectric 36 and focused on the plane of such storage dielectric by means of light source 48 and lens structure 52. The graticule light image produces a charge image of the graticule on the storage dielectric which is stored if its potential is suflicient and the voltage of the conductive areas is above the retention threshold voltage.

A light image of low intensity may be stored on the storage dielectric 36 by employing the charge image integration technique referred to previously in which the flood electrons are prevented from striking the storage dielectric during the formation of the charge image corresponding to such light image. This may be accomplished by cutting off the flood guns such as by connecting the control grids 30 of the flood guns to a more negative DC. voltage source of about 75 volts through a twoposition selector switch 90 in the integrate position of such selector switch. After the light image has raised the potential of its charge image sufliciently to be stored on the storage dielectric 36, the selector switch 90 is moved back to the store position to connect the control grids of the flood guns to a negative DC. voltage of about --25 volts. This more positive control grid voltage enables the flood electrons emitted by the cathodes 20 to bombard the storage dielectric to store the charge image corresponding to the light image of the graticule scale in the conventional bistable manner.

After the charge images of the signal waveforms and graticule scale have been stored on the storage target 12, such images may be viewed directly through the face plate 16 of the storage tube when the photosensitive storage dielectric 36 is phosphor material. In addition, the stored charge images can be reproduced on a remote display device such as television monitor 56 by performing an electrical readout operation. Electrical readout is accomplished by moving the selector switches 74 and to the read positions to connect the vertical deflection plates 26 and the horizontal deflection plates 24 to a raster signal genera-tor 9-2 in order to scan the electron beam across the storage dielectric. At the same time, the selector switch 84 is moved to the read position to conmeet the control grid 20 of the electron gun to a more negative voltage of about 3050 volts in order to decrease the current density of such electron beam. The raster signal generator 92 is also connected to the horizontal and vertical deflection plates of monitor tube 56 and may be of a conventional type used in television receivers which produces a vertical sawtooth signal having a frequency of 60 cycles per second and a horizontal sawtooth signal having a frequency of about 15,750 cycles per second.

As the reading beam is scanned across the charge image on the storage dielectric, it causes secondary electrons to be emitted from such dielectric and produces an electrical readout signal on conductive areas 38 and 40 corresponding to the charge images. These electrical readout signals are transmitted through A.C. coupling capacitors 94 and 96 connected to conductive areas 38 and 40, respectively, to amplifier 58. The amplified readout signals are applied to the Z-axis input of the television monitor 56 in order to modulate its brightness as the electron beam of such monitor tube is scanned by the raster signal generator 92. As a result, the images of the reference signal 86 and the comparison signal 88 are both reproduced on the viewing screen of the monitor tube 56. In addition, a graticule scale image 98 is produced on such monitor tube, corresponding the the charge image of the graticule scale stored on the photosensitive storage dielectric 36 of storage tube 10.

In addition to the graticule scale, the photographic film negative 50 may also be provided with an image of the setting of the switch adjusting the gain of the vertical amplifier 72 in order to indicate the units of the vertical axis of the graticule scale. As a result such switch position is stored as a charge image on the storage dielectric 36 and reproduced on the monitor tube 56 during electrical readout as a switch position display 100 shown as mv./cm., which indicates that each vertical centimeter is equal to 10 millivolts. A second switch position image can be stored in a similar manner on the storage target to indicate the sweep speed of the horizontal sweep generator 78. Such horizontal sweep speed setting is then reproduced as a second switch position display 102 on the monitor tube 56, and shown as 50 ,us/cm., indicating that each horizontal centimeter of the graticule scale is equal to 50 microseconds.

As stated previously, the pointer light 54 may be employed during electrical readout to produce a pointer spot charge image on the storage target which is electrically read out and transmitted to the monitor tube, Where it is reproduced as a pointer spot 104 on the viewing screen to indicate a particular portion of the signal waveform 88. As indicated by the dashed lines, the pointed spot may be first located in a position 104' without storing such spot and subsequently moved to position 104 without obscuring the stored charge images.

When the electrical readout operation is completed, the selector switches 74, 80 and 84 are moved back to their write positions. The stored charge images are erased off the storage target 12 by varying resistances 60 and 62 to first increase the DC. voltage on conductive areas 38 and 40 above the fade positive potential and then to decrease such voltage below the retention threshold potential before returning such voltages to the stable range between the retention threshold voltage and the fade positive voltage. It should be noted that this erasing operation can be performed by electronic switching circuits, ascan the operation of switches 74, 80 and 84 and switch 90.

As shown in FIG. 2, the storage apparatus of FIG. 1 can be modified by eliminating the focusing lens 52 if a collimated or point light source 106 is employed in place of light source 48. One such collimated light source would be a laser, but the intensity of the light beam emitted by such laser must not be too great or it may cause damage to the light mask 50 and the storage target 12. In addition, a light image of a book page or other document can be produced by reflecting light directly oil of such document onto the front of the photosensitive storage dielectric, in which case the light source 106 can be moved to the dash line position 106'. Furthermore,

it is also possible to provide a light transparent window in the funnel portion of the storage tube envelope in order to project a light image through the side of the storage tube onto the rear surface of the storage dielectric.

As shown in FIG. 3, the storage apparatus in FIG. 1 may also be employed to store an X-ray image by using an X-ray source 108. Such X-ray source may be of a conventional continuously operating type employing a heated cathode and producing low intensity X-rays, or may be a pulsed X- ray tube employing a field emission cathode structure, which produces a short X-ray pulse of extremely high intensity. The X-rays are transmitted through a living or inanimate object 110 to produce an X-ray image of such object which is directed onto the photosensitive storage dielectric of storage target 12 to produce a charge image which is stored on such target. It has been found that the charge image integration technique referred to above is extremely helpful in storing the charge image corresponding to a low intensity X-ray image and because of the storage of such X-ray image reduces X-ray exposure of the object.

Another modification of the storage apparatus of FIG. I

1 is shown in FIG. 4 and includes a storage tube 10", having an interanl graticule scale 112 including graticule lines formed on the inner surface of the glass face plate 16 beneath conductive coatings 38 and 40. Such graticule lines may be provided by chemically etching the face plate or by printing a line pattern of glass frit, titanium dioxide or other light reflecting material on such face plate. In addition, the graticule scale lines 112 may also be provided by first etching the face plate to form notches and then filling the notches with titanium dioxide in order to provide a flat surface free of discontinuities which might otherwise change the thickness of the storage dielectric 36 and undesirably affect the operation of the storage target. The internal graticule 112 is ordinarily illuminated to a relatively low intensity by transmitting light through. the outer edge of the face plate 16 from an incandescent light bulb 114. The filament of bulb 114 is connected in series with a battery 116 or other low voltage source and a variable resistance 118, whose setting changes the intensity of the light emitted by such filament. In addition, a second more intense light source 120, which maybe a gas tube or spark gap, is provided in order to illuminate the graticule scale 112 through the outer edge of the face plate 16 for a. brief period of time to cause the light image of such graticule scale to produce a charge image on the storage dielectric 36 of sufficient potential to be stored in the manner previously described. The high intensity light source 120 is connected to a high voltage pulse generator (122 by a switch 124 in order to apply high voltage pulses to the gas tube or spark gap when the switch is in the on position. After the light image of the graticule scale is stored on the photosensitive storage dielectric 36 of the storage target, the switch 124 is moved back to the off position to reduce the intensity of the illuminated graticule scale to the comfortable viewing level of light bulb 114.

It will be obvious to those having ordinary skill in the art that many changes may be made in the above described embodiments of the present invention not departing from the spirit of the invention. Therefore, the scope of the present invention should only be determined by the following claims.

I claim:

1. Charge image storage apparatus capable of bistable storage comprising:

a storage target including a photosensitive storage dielectric of phosphor material;

light writing means for directing a light image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said light image; and

means-for bombarding the storage dielectric with low velocity electrons to cause secondary electrons to be emitted from said storage dielectric in the region of the charge image, and for collecting said secondary electrons to enable bistable storage of said charge image.

2. Charge image storage apparatus capable of bistable storage comprising:

a storage target including a photosensitive storage dielectric of phosphor material;

light writing means for directing a light image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said light image;

means for bombarding the storage dielectric with low velocity electrons to cause secondary electrons to be emitted from said storage dielectric in the region of the charge image, and for collecting said secondary electrons to enable bistable storage of said charge image if the potential of said charge image is greater than the first cross-over potential of the secondary emission characteristic of said storage dielectric; and

electrical readout means for scanning said storage dielectric with a beam of electrons in a predetermined manner to produce an electrical readout signal corresponding to said charge image.

3. Charge image storage apparatus capable of bistable storage comprising:

a storage target including a photosensitive storage dielectric of phosphor material;

light writing means including a light source separate from said storage dielectric, for directing a light image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said light image; and

means for bombarding the storage dielectric with low velocity electrons to cause secondary electrons to be emitted from said storage dielectric in the region of the charge image, and for collecting said secondary electrons to enable bistable storage of said charge image and to cause the phosphor storage dielectric to emit a light image corresponding to said charge image.

4. Charge image storage apparatus comprising:

a cathode ray storage tube capable of bistable storage and having a storage target including a photosensitive storage dielectric of phosphor material;

light writing means for producing a light image and for directing said light image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said light image;

electron writing means for producing an electron image and for directing said electron image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said electron image; and

means separate from said electron writing means, for bombarding the storage dielectric with low velocity electrons to cause secondary electrons to be emitted from said storage dielectric in the region of the charge images on said storage dielectric, and for collecting said secondary electrons to enable bistable storage of said charge images and to cause the phosphor storage dielectric to emit a light image corresponding to the stored charge images.

5. Charge image storage apparatus capable of bistable storage comprising:

a storage target including a photosensitive storage dielectric of phosphor material;

means for producing a light image and for directing said light image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said light image;

means for producing an electron image and for directing said electron image onto the storage dielectric to produce a charge image on said storage dielectric which corresponds to said electron image;

means for bombarding the storage dielectric with low velocity electrons to cause secondary electrons to be emitted from said storage dielectric in the region of the charge images on said storage dielectric, and for collecting said secondary electrons to enable bistable storage of said charge images and to cause the phosphor storage dielectric to emit a light image corresponding to the stored charge images;

readout means for scanning said storage dielectric with a beam of electrons in a predetermined manner to produce an electrical readout signal corresponding to said charge images; and

monitor means remote from said storage target, for

converting said readout signal into light images corresponding to said charge images.

6. A charge image storage apparatus comprising:

a cathode ray storage tube capable of bistable storage and having a storage target including a light transparent support member of insulating material, a light transparent electrically conductive coating on one side of said support member, a photosensitive storage dielectric in the form of an integral layer of phosphor material supported over said conductive coating on said one side of said support member;

said phosphor layer having a sufficiently thin and porous structure to enable secondary electrons emitted from one side of the layer to be transmitted through said layer and collected by the conductive coating on the other side of said layer and to enable bistable storage of a charge image on the phosphor layer while also emitting a light image corresponding to said charge image;

light means external of said storage tube for producing a light image and for projecting said light image directly onto the photosensitive phosphor layer to produce a first charge image on said phosphor layer corresponding to said light image;

writing means internal of said storage tube for producing an electron beam and for deflecting said electron beam across said phospher layer in accordance with an electrical input signal to form a second charge image on said layer corresponding to said input signal;

holding means for bombarding the phosphor layer with low velocity electrons to cause bistable storage of the charge images formed thereon Whose potential is above the first cross-over potential of the secondary emission characteristic of said phosphor layer;

readout means for scanning an electron beam in a predetermined manner across the phosphor layer of the storage target to produce an electrical readout signal on the conductive coating of such target, said readout signal corresponding to the charge images stored on said target; and

monitor means connected to said conductive coating of said storage target and to said readout means, for converting the electrical readout signal of the storage tube into a light image display which is a reproduction of the charge images on said target.

7. A charge image storage apparatus comprising:

a cathode ray storage tube capable of bistable storage having a storage target including a light transparent support member of insulating material, a light transparent eletrically conductive coating on one side of said support member, a photosensitive storalge dielectric in the form of an integral, porous layer of phosphor material supported over said conductive coating on said one side of said support member;

said phosphor layer having a sufficiently thin and porous structure to enable secondary electrons emit ted from one side of the layer to be transmitted through said layer and collected by the conductive coating on the other side of said layer and to enable bistable storage of a charge image on the phosphor layer while also emitting a light image corresponding to said charge image;

light means external of said storage tube for producing a light image and for projecting said light image directly onto the photosensitive phosphor layer to produce a first charge image on said phosphor layer corresponding to said light image;

avriting means internal of said storage tube for producing an electron beam and for deflecting said electron beam across said phosphor layer in accordance with an electrical input signal to form a second charge image on said layer corresponding to said input signal;

holding means for bombarding the phosphor layer with low velocity electrons to cause bistable storage of the charge images formed thereon whose potential is above the first cross-over potential of the secondary emission characteristic of said phosphor layer;

tube into a light image display which is a reproduction of the charge images on said target. 9. A method of storing a light image and an electron image as charge images on the same storage target of a cathode ray storage tube, comprising the steps of:

directing a light image onto a photosensitive storage dielectric of phosphor material in said target to produce a first charge image on said storage dielectric corresponding to said light image;

directing an electron image onto said storage dielectric to produce a second charge image on said storage dielectric corresponding to said electron image; and

bombarding said storage dielectric with low velocity electrons to cause secondary electron emission from the region of the charge images to enable bistable storage of said charge images and to cause the storage dielectric to emit light images corresponding to the stored charge images.

10. A method of storing a light image and an electron image as charge images on the same storage target of a cathode ray storage tube and reproducing said images on a display device remote from said target, comprising the steps of:

and integration means for preventing said low velocity electrons from striking the phosphor layer during the formation of said charge images until the potential of at least some of the charge images exceeds said first cross-over potential. 8. A charge image storage apparatus having electrical readout, comprising:

a cathode ray storage tube capable of bistable storage and having a storage target including a light transparent support member of insulating material, a light transparent electrically conductive coating on one side of said support member, said coating being divided into a plurality of insulatingly spaced conductive areas, a photosensitive storage dielectric in the form of an integral layer of phosphor material supported over said conductive coating on said one side of said support member;

said phosphor layer having a sufliciently thin and porous structure to enable secondary electrons emitted from one side of the layer to be transmitted through said layer and collected by the conductive coating on the other side of said layer and to enable bistable storage of a charge image on the phosphor layer while also emitting a light image corresponding to said charge image;

directing a light image onto a photosensitive storage dielectric of phosphor material in said target to produce a first charge image on said storage dielectric corresponding to said light image;

directing an electron image onto said storage dielectric to produce a second charge image on said storage dielectric corresponding to said electron image;

bombarding said storage dielectric with low velocity electrons to cause secondary electron emission from the region of the charge images to enable bistable storage of said charge images and to cause said storage dielectric to emit light images corresponding to the stored charge images;

scanning a beam of electrons across said storage dielectric in a. predetermined manner to produce an electrical readout signal corresponding to all of said charge images; and

transmitting said readout signal to a display device remote from said storage tube in order to reproduce said light image and said electron image on said display device.

11. A method of storing a light image and an electron image as charge images on the same storage target of a cathode ray storage tube and reproducing said images on a display device remote from said target, comprising the steps of:

light means external of said storage tube for producing a light image and for projecting said light image directly onto the photosensitive phosphor layer to produce a first charge image on said phosphor layer corresponding to said light image;

writing means internal of said storage tube 'for producing an electron beam and for deflecting said electron beam across said phosphor layer in accordance with an electrical input signal to form a second charge image on said layer corresponding to said input signal;

connection means for connecting the plurality of conductive areas of the storage target to difierent voltages to enable the regions of the phosphor layer above said conductive areas to operate independently in a storage or a nonstorage mode; and

holding means for bombarding the phosphor layer with low velocity electrons to cause bistable storage of the charge images formed thereon whose potential is above the first cross-over potential of the secondary emission characteristic of said phosphor layer;

readout means for scanning an electron beam in a predetermined manner across the phosphor layer of the storage target to produce an electrical readout signal on the conductive areas of such target, such readout signal corresponding to the charge images stored on said target; and

monitor means connected to said conductive areas of said storage target and to said readout means, for converting the electrical readout signal of the storage directing a light image onto a photosensitive storage dielectric in said target to produce a first charge image on said storage dielectric corresponding to said light image;

directing an electron image onto said storage dielectric to produce a second charge image on said storage dielectric corresponding to said electron image;

bombarding said storage dielectric with low velocity electrons to cause secondary electron emission from the region of the charge images to enable bistable storage of said charge images for a controllable time;

directing a beam of low intensity light onto said storage dielectric to produce a third charge image in the form of a pointer spot which is of insuflicient potential to be stored;

scanning a beam of electrons across said storage dielectric in a predetermined manner to produce an electrical readout signal corresponding to all of said charge images; and

transmitting said readout signal to a monitor device remote from said storage tube in order to reproduce said light image and said electron image on said monitor device.

12. A method of storing a light image and an electron image as charge images on the same storage target of a cathode ray storage tube and reproducing said images on a display device remote from said target, comprising the steps of:

directing a light image onto a photosensitive storage dielectric of phosphor material in said target to produce a first charge image on said storage dielectric corresponding to said light image; directing an electron image onto said storage dielectric to produce a second charge image on said storage dielectric corresponding to said electron image; bombarding said storage dielectric with low velocity electrons to cause secondary electron emission from the region of the charge images to enable bistable storage of said charge images and to cause said storage dielectric to emit light images corresponding to the stored charge images; preventing said low velocity electrons from bombarding the storage dielectric during the formation of the charge images corresponding to said light image and said electron image until the potentials of the charge images exceed the minimum voltage necessary for bistable storage;

References Cited UNITED STATES PATENTS Anderson 315-42 Goodrich 315-12 Toohig et al. 31367 X Kazan 315--12 RODNEY D. BENNETT, Primary Examiner.

JEFFREY P. MORRIS, Assistant Examiner.

US. Cl. X.R. 

